1. Field of the Invention:
This invention relates to an automatic package machine for wrapping an article by drawing a wrapping film from a roll , placing the article in the film, and then fusing and sealing the film at predetermined positions to form a bag, and also to a wrapping film fusing and sealing blade for use in the automatic package machine. More particularly, the invention relates to an automatic package machine equipped with means for reliably fusing and sealing edge portions of upper and lower film parts, irrespective of the shape and size of the article to be wrapped, and also to a wrapping film fusing and sealing blade as the fusing and sealing means.
2. Description of the Related Art:
An automatic package machine developed by the present inventor(s) and using a folded film is known from, for example, Japanese Utility Model Publication No. SHO 62-18429. According to the prior art automatic package machine, an L-type sealing unit having a wrapping film fusing and sealing blade seals the folded film openings perpendicular and parallel to the folding direction of the film simultaneously.
However, for reliably fusing and sealing the two film parts simultaneously, it is essential that air should not exist between the two film parts inside the fused and sealed portion. If air exists between the film parts inside the fused and sealed portion, the two film parts would be locally peeled off in the operative portion of the fusing and sealing blade so that fusing and melting will proceed with the upper and lower film parts only partially sealed. Accordingly the upper and lower film parts would be locally unsealed; that is, a so-called pin hole phenomenon would occur to cause imperfect sealing.
With the above-mentioned L-type sealing unit in particular, since the film parts are fused and sealed longitudinally and transversely of the travelling path of the film, air existing between the two film parts would increase in pressure, as kept in the sealed portion during sealing, thus urging to spread the sealed film parts. Further, if the article is to be wrapped in film by the L-type sealing unit in such a manner that the film is brought against the article as closely as possible, and particularly if the height of the article is relatively large, the film would inevitably be deformed on a large scale. This would result in imperfect sealing. Consequently, it has been customary to provide a pair of film pressers one on each side of the wrapping film fusing and sealing means to clamp the fused and sealed portions of the film parts between the film pressers and a receiving member, thus eliminating the air while fusing and sealing. By this mechanical pressing, it would be difficult to achieve a perfect contact between the two film parts, even with the use of a highly precise mechanical process, so that the above-mentioned problems cannot be avoided on many occasions. It is therefore necessary to use a film wider than necessary in order to increase the distance between the sealing lines and an article to be wrapped, thus not only marring the appearance of the wrapped product but also increasing the amount of film consumption.
For the automatic package machine employing a sealing unit other than the above-mentioned L-type sealing unit, it is known to place the article between two elongated films superposed or two parts of a film folded and to perform sealing of the upstream and downstream ends independently of the sealing of one or both of side edges. It is known that the upstream and downstream ends are sealed by a so-called I-type sealing unit using a straight heat bar, while the individual side edge is sealed by upper and lower sealing discs rotating along the sealing line between a horizontal pair of upper endless belts and a horizontal pair of lower endless belts while the two films or film parts are clamped and conveyed thereby. According to this sealing method, since the upstream and downstream ends or the side edge(s) are open during sealing the edge(s) or ends, the influence by the air existing between the films or film parts is small, compared with that of the L-type sealing unit.
As an alternative, a pyro-electric package machine, which charges merely static electricity on the upper and lower film parts and joins the opening edge portions of the upper and lower film parts by electrostatic sealing without tile above-mentioned heating means, is disclosed in, for example, Japanese Patent Publication No. SHO 63-17696.
However, in the package machine which performs the sealing of the upstream and downstream ends and the sealing of the side edges individually by fusing and sealing, each side of the film parts is brought into contact with one another mechanically by the film presser and endless belts while the intermediate portions of the two film parts are unsealed. This allows air to exist between the film parts so that the above-mentioned pin holes can not be perfectly eliminated.
Specifically, with the side edge sealing unit, since the film side edge portions to be sealed are pressed against one another between the upper and lower endless belts, it is necessary to push the upper and lower belts Uniformly along the entire length of the belts on the film travelling side in order to obtain a uniform contact. However, partly since endless belts tend to become loose and partly since the upper and lower sealing discs are situated between the endless belts, it is very difficult to achieve a uniform contact between the two film parts.
In this kind of automatic continuous package machine, it is inevitable that the travelling of the film is temporarily stopped when the two film parts are sealed at least in a direction perpendicular to the travelling path of the film. At that time the upper and lower sealing discs must be temporarily separated from the film surfaces. If the sealing discs are not separated from the film surfaces, the melted portions would be enlarged to be carbonized while the two film portions compressed by the upper and lower sealing discs are separated, so that such portions would have pin holes, thus making the sealing untidy.
On the other hand, according to the electrostatic sealing, since the upper and lower film parts adhere to each other merely electrostatically, they can be sealed reliably, as disclosed in the above-mentioned publication, when shrunk in a subsequent stage of process; if not shrunk, they tend to be separated so that adequate sealing cannot be expected. Even if they are shrunk, e.g., when an article to be wrapped contains much water, static electricity on the film would be eliminated due to the water so that the adhesion will disappear at all and, as a result, adequate sealing cannot be expected.